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To:     "Boris Brezillon" <boris.brezillon@collabora.com>
Cc:     bbrezillon@kernel.org, computersforpeace@gmail.com,
        dwmw2@infradead.org, frieder.schrempf@kontron.de,
        gregkh@linuxfoundation.org, juliensu@mxic.com.tw,
        linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org,
        marcel.ziswiler@toradex.com, marek.vasut@gmail.com,
        "Miquel Raynal" <miquel.raynal@bootlin.com>, richard@nod.at,
        tglx@linutronix.de, vigneshr@ti.com
Subject: Re: [PATCH RFC 3/3] mtd: rawnand: Add support Macronix power down mode
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From:   masonccyang@mxic.com.tw
Date:   Fri, 25 Oct 2019 11:11:13 +0800
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Hi Boris,

> 
> Subject
> 
> Re: [PATCH RFC 3/3] mtd: rawnand: Add support Macronix power down mode
> 
> On Tue, 8 Oct 2019 10:06:50 +0800
> masonccyang@mxic.com.tw wrote:
> 
> > > > +   nand_select_target(chip, 0); 
> > > 
> > > On several NAND controllers there is no way to act on the CS line
> > > without actually writing bytes to the NAND chip. So basically this
> > > is very likely to not work. 
> > 
> > any other way to make it work ? GPIO ?
> > or just have some comments description here.
> > i.e,.
> > 
> > /* The NAND chip will exit the deep power down mode with #CS toggling, 

> >  * please refer to datasheet for the timing requirement of tCRDP and 
tRDP.
> >  */
> > 
> 
> Good luck with that. As Miquel said, on most NAND controllers
> select_target() is a dummy operation that just assigns nand_chip->target
> to the specified value but doesn't assert the CS line. You could send a
> dummy command here, like a READ_ID, but I guess you need CS to be
> asserted for at least 20ns before asserting any other signals (CLE/ALE)
> which might be an issue.
> 

I have validated & checked w/ designer that NANDs device just need CS# 
line
toggling and don't care of CLE/WE#/RE#. That is raw NAND controller 
sending
a command nand_status_op() or nand_power_down_op() will exit the deep 
power down too. The first command(just CS# line toggling) to NAND device 
in deep power down mode will not be recognized. We may publish the 
application notes or update the datasheet later.

thanks & best regards,
Mason

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